Lighting domes with reflective gradient and broad spectrum light source

ABSTRACT

A lighting dome that can be used to inspect semiconductor wafers can include a small aperture, backlighting, a reflectance gradient and/or a broad spectrum light source.

CROSS-REFERENCE TO RELATED APPLICATION

Referring to the application data sheet filed herewith, this applicationis a continuation of, and claims a benefit of priority under 35 U.S.C.120 from copending utility patent application U.S. Ser. No. 13/826,973,filed Mar. 14, 2013 the entire contents of which are hereby expresslyincorporated herein by reference for all purposes.

BACKGROUND

Prior art lighting domes, are known to those skilled in the art ofphotography. There are commercial domes for viewing semiconductor wafersthat have a large hole in them for the lens to view through. Forinstance, a conventional dome reflector is typically a hollowhemispherical shell with a reflectively coated interior. Lights locatedalong the interior rim of the shell reflect off the interior toilluminate an object to be viewed. For shiny spherical and convexobjects, dome illuminations provide a somewhat diffuse and homogeneouslight with less reflection.

Conventional optical systems use a lens with a front element whose sizedetermines the aperture on the dome required to view the wafer. As thisaperture size is increased the reflection of the lens in the image ofthe wafer makes a significant portion of the image unusable. To overcomethis and other issues, U.S. Pat. No. 5,684,530 describes a secondoptical arrangement over the aperture in the dome to allow theillumination of the central spot with a second light source.

However, the disadvantages of this second optical arrangement includethe following difficulties. The lighting in the central part throughwhich the camera views the object is not truly multi-directional. Thelighting for the central part is from a different light source so thecolors and the intensities must be matched to that of the source for thedome making it difficult to use in practice. The height of the lightsource is increased. The beam-splitter through which the camera viewsthe object can introduce changes to the light passing through it andobstruct the view of the object. What is needed is lighting dometechnology that addresses the above-discussed issues in a cost-effectivemanner.

Meanwhile, the challenges of visual inspection or macro-inspection ofsemiconductor wafers an applet, a servlet, a source code, an objectcode, a shared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer or computer system).

The term substantially is intended to mean largely but not necessarilywholly that which is specified. The term approximately is intended tomean at least close to a given value (e.g., within 10% of). The termgenerally is intended to mean at least approaching a given state. Theterm coupled is intended to mean connected, although not necessarilydirectly, and not necessarily mechanically. The term proximate, as usedherein, is intended to mean close, near adjacent and/or coincident; andincludes spatial situations where specified functions and/or results (ifany) can be carried out and/or achieved. The term distal, as usedherein, is intended to mean far, away, spaced apart from and/ornon-coincident, and includes spatial situation where specified functionsand/or results (if any) can be carried out and/or achieved. The termdeploying is intended to mean designing, building, shipping, installingand/or operating.

The terms first or one, and the phrases at least a first or at leastone, are intended to mean the singular or the plural unless it is clearfrom the intrinsic text of this document that it is meant otherwise. Theterms second or another, and the phrases at least a second or at leastanother, are intended to mean the singular or the plural unless it isclear from the intrinsic text of this document that it is meantotherwise. Unless expressly stated to the contrary in the intrinsic textof this document, the term or is intended to mean an inclusive or andnot an exclusive or. Specifically, a condition A or B is satisfied byany one of the following: A is true (or present) and B is false (or notpresent), A is false (or not present) and B is true (or present), andboth A and B are true (or present). The terms a and/or an are employedfor grammatical style and merely for convenience.

The term plurality is intended to mean two or more than two. The termany is intended to mean all applicable members of a set or at least asubset of all applicable members of the set. The term means, whenfollowed by the term “for” is intended to mean hardware, firmware and/orsoftware for achieving a result. The term step, when followed by theterm “for” is intended to mean a (sub)method, (sub)process and/or(sub)routine for achieving the recited result. Unless otherwise defined,all technical and scientific terms used herein have the same meaning ascommonly understood by one of ordinary skill in the art to which thispresent disclosure belongs. In case of conflict, the presentspecification, including definitions, will control. include thefollowing issues. The produce can change from one batch to another,thereby changing the expectation of what a good wafer looks like. Theproduct is highly reflective so it is difficult to illuminate withoutglares. A defect can be hard to define, especially when the failuremechanism is not known. These challenges make manual inspection of thewafers the industry default macro-inspection. But a disadvantage of thisapproach has been relatively high cost. What is needed is a waferinspection solution that obviates the above-discussed issues in acost-effective manner.

SUMMARY

There is a need for the following embodiments of the present disclosure.Of course, the present disclosure is not limited to these embodiments.

According to an embodiment of the present disclosure a method, comprisesilluminating a reflective dome with light from a light source;Illuminating an object substantially homogeneously with light reflectedby the reflective dome; and sensing light from the object through asmall aperture in the reflective dome. According to an embodiment of thepresent disclosure, an apparatus, comprises: a reflective dome defininga small aperture; and a light source coupled to the reflective dome.

According to an embodiment of the present disclosure a method, comprisesilluminating a reflective dome with light from a light source;Illuminating an object substantially homogeneously with light reflectedby the reflective dome; and sensing light from the object through anaperture in the reflective dome, wherein the object is located betweenthe broad spectrum light source and the reflective dome. According to anembodiment of the present disclosure an apparatus comprises: areflective dome defining an aperture; a light source coupled to thereflective dome; and an object holder located between the broad spectrumlight source and the reflective dome.

According to an embodiment of the present disclosure a method comprisesilluminating a reflective dome having a reflectance gradient with lightfrom a light source; Illuminating an object substantially homogeneouslywith light reflected by the reflectance gradient of the reflective dome;and sensing light from the object through an aperture in the reflectivedome. According to an embodiment of the present disclosure an apparatus,comprises: a reflective dome having a reflective gradient and definingan aperture; and a light source coupled to the reflective dome.

According to an embodiment of the present disclosure a method comprisesilluminating a reflective dome with light from a broad spectrum lightsource; Illuminating an object substantially homogeneously with lightreflected by the reflective dome; and sensing light from the objectthrough an aperture in the reflective dome. According to an embodimentof the present disclosure an apparatus, comprises a reflective domedefining an aperture; and a broad spectrum light source coupled to thereflective dome.

According to an embodiment of the present disclosure, a method,comprises illuminating a reflective dome having a reflectance gradientwith light from a broad spectrum light source; Illuminating an objectsubstantially homogeneously with light reflected by the reflectancegradient of the reflective dome; and sensing light from the objectthrough a small aperture in the reflective dome, wherein the object islocated between the broad spectrum light source and the reflective dome.According to an embodiment of the present disclosure, an apparatus,comprises: a reflective dome having a reflective gradient and defining asmall aperture; a broad spectrum light source coupled to the reflectivedome; and an object holder located between the broad spectrum lightsource and the reflective dome.

These, and other, embodiments of the present disclosure will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. It should beunderstood, however, that the following description, while indicatingvarious embodiments of the present disclosure and numerous specificdetails thereof, is given for the purpose of illustration and does notimply limitation. Many substitutions, modifications, additions and/orrearrangements may be made within the scope of embodiments of thepresent disclosure, and embodiments of the present disclosure includeall such substitutions, modifications, additions and/or rearrangements.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings accompanying and forming part of this specification areincluded to depict certain embodiments of the present disclosure. Aclearer concept of the embodiments described in this application will bereadily apparent by referring to the exemplary, and thereforenonlimiting, embodiments illustrated in the drawings (wherein identicalreference numerals (if they occur in more than one view) designate thesame elements). The described embodiments may be better understood byreference to one or more of these drawings in combination with thefollowing description presented herein. It should be noted that thefeatures illustrated in the drawings are not necessarily drawn to scale.

FIG. 1 is a schematic side view of a lighting dome that includes a domereflector and a back light source.

FIG. 2A is a schematic side view of a lighting dome that includes a domereflector having a gradient reflector interior surface and a back lightsource.

FIG. 2B is an illustration of flux of light incident on the gradientreflector interior surface as a function of position relative to thebase plane defined by the edge of the dome reflector.

FIG. 2C is an illustration of thickness/reflectively of the dome as afunction of position relative to the base plane defined by the edge ofthe dome reflector.

FIG. 2D is an illustration of flux of light incident on the wafer (or aplane defined by the wafer) as a function of position relative to thebase plane defined by the edge of the dome reflector.

FIG. 3A is a machine vision image of a wafer illuminated by red light(i.e., narrow spectrum) showing an elliptical shaped pattern than cancause a false positive when testing for defects and/or residue.

FIG. 3B is a machine vision image of a wafer illuminated by white light(i.e., relatively broad spectrum) that does not show the patternmentioned above with regard to FIG. 3A.

DETAILED DESCRIPTION

Embodiments presented in the present disclosure and the various featuresand advantageous details thereof are explained more fully with referenceto the nonlimiting embodiments that are illustrated in the accompanyingdrawings and detailed in the following description. Descriptions of wellknown starting materials, processing techniques, components andequipment are omitted so as not to unnecessarily obscure the embodimentsof the present disclosure in detail. It should be understood, however,that the detailed description and the specific examples are given by wayof illustration only and not by way of limitation. Varioussubstitutions, modifications, additions and/or rearrangements within thescope of the underlying inventive concept will become apparent to thoseskilled in the art from this disclosure.

The below-referenced U.S. Patent(s) and/or U.S. Patent Application(s)disclose embodiments that are useful for the purposes for which they areintended. The entire contents of U.S. Pat. No. 5,684,530 are herebyexpressly incorporated by reference herein for all purposes. The entirecontents of U.S. Ser. No. 12/704,383 filed Feb. 11, 2010 (U.S. Pat. App.Pub. 2010/0208980, published Aug. 19, 2010) are hereby expresslyincorporated by reference herein for all purposes.

Overview

In general, the context of embodiments of the present disclosure caninclude inspection of semiconductor fabrication wafers. Embodiment ofthe present disclosure can include a machine vision system. The machinevision system can include a lighting dome. The lighting dome can includea reflective dome (dome reflector). The reflective dome can have asubstantially circular edge defining a base plane. The reflective domecan be placed above (over) a semiconductor wafer (or other object ofinterest to be viewed). The lighting dome can include one or moreopenings to view the semiconductor wafer. The lighting dome can includeone or more light source(s) that are incident upon the reflective dome.The reflected light from the reflective dome can then in-turn illuminatethe semiconductor wafer or other object of interest.

More specially, the context of embodiments of the present disclosure caninclude detection of defects in the manufacturing of semiconductorwafers. This defect detection can be performed one or more times duringprocessing of the wafer itself and/or one or more times duringprocessing of the circuits that are fabricated on the wafer. This defectdetection can be performed after processing of the wafer itself iscomplete and/or after processing of the circuits is complete; beforedicing the wafer into individual chips.

For instance, the context of embodiments of the disclosure can includedetection of residue on the surface of semiconductor wafers. Thisresidue detection can be performed one or more times during processingof the wafer itself and/or one or more times during processing of thecircuits that are fabricated on the wafer. This residue detection can beperformed after processing of the wafer itself is complete and/or afterprocessing of the circuits is complete; before dicing the wafer intoindividual chips.

Small Aperture Reflective Dome

The reflective dome can include an opening at or near the top of thedome; and a camera lens located proximate the opening. The opening caninclude a small aperture through which the wafer is viewed with apinhole lens. The small aperture has the advantage of leaving more ofthe dome's reflective surface intact while still allowing the use of thepinhole lens. The use of the pinhole lens has the advantage of reducingthe amount of lens reflection on the surface of the wafer while stillallowing the use of the camera. The camera captures an image of thewafer and transfers it to a connected computer where a softwarealgorithm is used to detect variations in the pattern of the wafer. Thesmall aperture can be as small as less than approximately 1 degree (60minute of arc), preferably less than approximately 6 minutes of arc. Inpreferred embodiments, the opening is circular and located substantiallycoaxial with a normal to the base plane, that normal being substantiallycoaxial with a center of the circular edge.

For example, the aperture in the dome can be minimized to a diameter ofapproximately 3 mm from a diameter of approximately 25 mm resulting inthe following advantages. Approximately 98.56% of the previouslyunusable area is recovered. The area around the center of the dome hasthe same multi-directional illumination as the rest of the dome becauseit is not affected by the missing light from the area of the aperture.For an industry standard 200 mm wafer, 99.975% of the wafer can beinspected if the reflection of the aperture is limited to a 3 mm region.For an industry standard 300 mm wafer, 99.99% of the wafer can beinspected if the region of the aperture is considered unusable incontrast to 92.8% for a commercial dome. The small aperture to view thewafer can be used with the combination of a pinhole lens to view theentirety of the wafer. The size of the dome needed for an evenillumination can be minimized. For inspecting a 200 mm wafer the domeneeds to be 270 mm in contrast to a commercial dome that is 300 mm. Forinspecting a 300 mm wafer the dome needs to be 350 mm in contrast to acommercial dome that is 424 mm.

An exemplary lighting geometry is shown in FIG. 1. A white light source110 is a flat, diffuse ring light that is directed towards an interiorof a dome reflector 120. The dome reflector is a white plastichemispherical shell with a diffuse interior surface and a small aperture130 at the top for viewing by a camera 140. In this example, the shellis of uniform thickness, but the shell can be of variable thickness toprovide a reflective gradient. In this example, the camera includes asensor without any optical filters, but the camera can include sensor(s)with optical filters (including color sensors, ultraviolet, Nearinfrared, etc.). The camera is not limited to a color camera. The camerais coupled to a pinhole lens 150 that is aligned with the small apertureto view a semiconductor wafer 160. In this example, the while lightsource is located in back of the wafer with regard to the camera.

Back Light Source(s)

Embodiments of the present disclosure can include a reflective dome thatis illuminated with lighting from behind (in back of) the wafer or otherobject of interest. Embodiments of the disclosure can include one ormore light source(s) located below (behind) (in back of) the object tobe viewed (e.g. the wafer). This means that the wafer or other object ofinterest, is located between the lighting source(s) and the opening ofthe dome reflector. In this case, the one or more light source(s) can betermed back light(s). In preferred embodiments, the one or more lightsource(s) are also located below the base plane of the dome reflector.This means that the base plane of the dome reflector is located betweenthe lighting source(s) and the opening of the dome reflector.

Embodiments of the present disclosure can include the use of one or more(LED) light source(s) to create a backlit image of the wafer. Thissingle LED light source can be in the form of a homogeneous lightingpanel upon which the substrate (or other object) is located to beviewed. Embodiments of the present disclosure can include the use of adiffuse dome lit image of the wafer. The diffuse dome lit image can beobtained by coating the interior surface of reflective dome with a filmor layer that functions as a physical diffuser.

The light source behind the wafer (back lighting) results in at leastthe following advantages. A backlit image of the wafer is obtained whichallows for determination of the rotation of the wafer based on thelocation of the notch on the wafer. Substantially even illumination isobtained for the entire wafer for a smaller size of the dome relative tothe wafer. The wafer can be placed closer to the dome resulting in amore even illumination over the area of the wafer. Maintenance of thelight can be performed without affecting the optical alignment of thecamera, lens and the dome. A less expensive flat ring light can be usedas the light source. Heat from the light does not affect the dome thusallowing the dome to be made out of less expensive polymer than themetal domes used in commercial lights. The panel provides an angularlyhomogenous even light source that is then reflected off the domecompared to the discrete LED sources used to illuminate the commercialdomes. The panel can be polarized and the light incident on the interiorof the reflective dome and, therefore, be polarized.

The wafer or other object of interest that is lit with one or more backlight source(s) can be observed with a pinhole lens viewing through asmall aperture in the reflective dome. While the small aperture and backlight source(s) can be used together in combined embodiments, the smallaperture and back light source(s) are independent and separate elementsthat can be used alone in separate embodiments. This means thatembodiments of the present disclosure can include both or just one ofthe small aperture and/or the back light source(s).

Gradient Reflective Dome

Embodiment of the present disclosure can include a reflective dome thatis formed of a (co)polymer or other material that is partiallyreflective and partially transmissive (translucent). A truly diffusereflection can be obtained from the polymer dome because the light can(at least partially) penetrate the first surface of the dome and, inthis case, is not reflecting off a coating on a metallic surface. Byadjusting the shape, thickness, reflectivity of the inside and outsidesurface and the diameter of the dome relative to the wafer a radiallyeven illumination can be obtained. See FIG. 2. Note that the dome can beellipsoidal. While the back light panel may be polarized, the lightincident on the surface of the wafer can be random polarization with adiffuse inside surface of the dome acting to randomize the polarization.In this way, the polarization of the light incident on the wafer istruly random. Embodiments of the present disclosure can include alighting dome including a dome reflector having a reflectivity thatchanges as a function of an angle to a normal of the base plane, thisnormal being substantially coaxial with a center of the circular edge ofthe dome reflector. The term normal in this context means a geometricalline that is perpendicular to the base plane defined by the circularedge of the dome reflector. The phrase normal being substantiallycoaxial with an axis of the circular edge means the normal passesthrough a center defined by the circular edge. In preferred embodiments,the reflectivity of the dome reflector increases as the angle to thenormal decreases (i.e. increases toward the opening at the top of thedome).

In preferred embodiments, the increase in reflectivity is provided by anincrease in thickness of a polymer shell that forms the dome reflector.In this case, the reflectivity decreases as the thickness decreasestoward the circular edge. Alternatively, the change in reflectivity canbe provided by a reflective coating of variable composition (e.g. apaint with variable metal flake content). In this case, the metal flakecontent would increase toward the small aperture. Alternatively, thechange in reflectivity can be provided by a material (e.g. polymer)whose porosity decreases as the angle to the normal decreases.

Another exemplary lighting geometry is shown in FIG. 2. A white lightsource 210 is a flat, circular panel that is directed towards aninterior of a dome reflector 220. The dome reflector is a white plastichemispherical shell with a diffuse interior surface and a small aperture230 at the top for viewing by a camera (not shown in this illustration).In this example, the shell is of variable thickness that defines agradient that increases toward the small aperture to provide areflective gradient whereby the reflectivity increases toward the smallaperture. In this example, the camera includes a monochromatic sensor,but the camera can include color sensor(s) (2CCD or multispectral). Asemiconductor wafer 260 is located on an end-effector 270. In thisexample, the white light source is also located in back of the wafer.

FIG. 2B shows the flux of light incident on the gradient reflectorinterior surface as a function of position relative to the base planedefined by the edge of the dome reflector. The lower flux caused by theshadow cast by the wafer, and also the end-effector, can be seen. FIG.2C shows thickness/reflectivity of the dome as a function of positionrelative to the base plane defined by the edge of the dome reflector.The increase in reflectivity toward the top of the reflective dome dueto the increasing thickness can be seen. FIG. 2D shows flux of lightincident on the wafer (or a plane defined by the wafer) as a function ofposition relative to the base plane defined by the edge of the domereflector. The flat line shows uniform illumination.

The wafer or other object of interest that is illuminated with lightreflected by the gradient reflector dome can be observed with a pinholelens viewing through a small aperture in the reflective dome. The waferor other object of interest that is illuminated with light reflected bya the gradient reflector dome can be lit with one or more back lightsource(s).

While the small aperture, the back light source(s) and the gradientreflector can be embodied together in combined embodiments, the smallaperture, the back light source(s) and the gradient reflector areindependent and separate elements that can be used alone in separateembodiments or in subcombinations composing two out of three. This meansthat embodiments of the disclosure can include two, or just one of thesmall aperture, the back light source(s) and/or the gradient reflector.

Wide Spectrum Light Source(s)

Embodiments of the disclosure can include the use of white (broadspectrum) light reflected by the reflective dome to illuminate asemiconductor wafer or other object of interest. The wafer or otherobject of interest that is illuminated by one or more broad spectrum(white) light sources can be observed by a unfiltered (monochrome)camera. Thus, embodiments of the present disclosure can include the useof a white (broad spectrum) light source with a broad spectrumintegrating camera to integrate the image over a broad spectrum. The useof a broad spectrum light source can improve imaging results and thiswill be discussed below in more detail.

FIG. 3A shows a machine vision image of a wafer illuminated by red light(i.e., narrow spectrum) showing an elliptical shaped pattern than cancause a false positive when testing for defects and/or residue. FIG. 3Bshows a machine vision image of a wafer illuminated by white light(i.e., relatively broad spectrum) that does not show the patternmentioned above with regard to FIG. 3A. The image of FIG. 3B wasobtained using a broad spectrum integrating camera to integrate theimage over a broad spectrum.

The wafer or other object of interest that is illuminated by one or morebroad spectrum light sources can be observed with a pinhole lens viewingthrough a small aperture in the reflective dome. The wafer or otherobject of interest that is illuminated by one or more broad spectrumlight sources can be lit with one or more back light source(s). Thewafer or other object of interest can be illuminated with lightreflected by a gradient reflector dome.

While the small aperture, the back light source(s), gradient reflectorand wide spectrum sources(s) can be utilized together in combinedembodiments, the small aperture, the back light source(s), the gradientreflector and the wide spectrum source(s) are all independent andseparate features that can be embodied alone in separate embodiments orin subcombinations of two or three. This means that embodiments of thedisclosure can include three, two, or just one of the small aperture,the back light source(s), the gradient reflector and/or the widespectrum light source(s).

Residue Detection System

Embodiments of the present disclosure can include a residue detectionsystem (RDS). A residue detection system is a machine vision system usedto detect residual metal films on the surface of a semiconductor wafer.The lighting and optics for the vision system can be designed to: viewthe entire wafer and/or part of the wafer. To this end, the lighting andoptics illuminate the wafer evenly across the entire surface to helpcreate an image of the wafer with contrast between the residual metaland the rest of the wafer. The system can utilize one, two or moresoftware algorithms to detect the presence of the residue in theresulting image.

Alternatively, embodiments of the present disclosure can omit the use ofsoftware algorithms relying instead on raw data. Embodiments of thepresent disclosure can even omit the use of a camera or sensor relyinginstead on observation of the image produced by the lighting source(s),the object(s), the dome, and optionally a pin hole lens.

In those embodiments that utilize one, two or more software algorithms,a first algorithm can use a predetermined threshold to detect pixelsthat are above a specific (optionally predetermined) intensity. Thesepixels (areas) are determined (calculated) by the algorithm to be theresidual metal.

A second algorithm is designed to detect residue that has the sameintensity as the metallic traces on the wafer. The second algorithm:first determines the repeating pattern on the wafer; and second uses thescale of the pattern to look for differences between similar regions.The differences are determined to be regions where there is residualmetal. The sensitivity of this second algorithm is dependent on theuniformity of the lighting used to illuminate the wafer. If theillumination is not even, the second algorithm will detect this as aregion of difference that will result in a false detection of residualmetal.

The conventional method to produce a grayscale image with a monochromecamera is to use a monochromatic light source. When a monochrome camerais used to view the wafer with a monochromatic light, a grayscale imageis produced. Regions of the wafer that do not have a metallic residuereflect the light from the dome with a diffuse Lambertian reflectance.Regions of the wafer that have metallic residue reflect the light with aspecular reflection component added to the diffuse reflection. When athick layer of metal is present its specular reflection can be largeenough to cause a detectable increase in the intensity of that region.However, when the metal layer is thinner or has a diffuse finish, theintensity of the region is similar to that of the metallic tracesrunning across the wafer.

Referring to FIG. 3A, when the RDS system is built with a redmonochromatic source (660 nm) and a monochrome camera the image of somewafers exhibits a pattern that is aligned to the notch of the wafer.This “evil eye” pattern is related to the properties of the surface ofthe wafer and the dome used to illuminate the wafer. This pattern is notvisible in an image of the wafer without the dome. This pattern limitsthe ability of the algorithm(s) used to detect the residual defects asthis pattern causes false failures.

Referring to FIG. 3B, the use of white (broad spectrum) light source(s)with the dome and a broad spectrum integrating (color) camera eliminatesthe formation of the “evil eye” pattern. This greatly enhances thecapability of the RDS system as the algorithm does not have to bedesensitized to prevent false failures caused by this pattern. The “evileye” pattern is also sometimes visible in images of the wafer obtainedwith a white light and a monochromatic camera. However, via the use of anon-monochromatic camera the intensity of the pattern is greatly reducedin each color plane. Each pixel in a color camera integrates the part ofthe spectrum of light that is passed by the filter in front of it (red,green or blue). In contrast to a monochromatic light source the broadspectrum of light for each pixel reduces the formation of the pattern.It is important to appreciate that when a white light is used with abroad spectrum integrating camera the pattern is eliminated because ofthe integration over the entire spectrum at each pixel.

As previously noted, the challenges of visual inspection ormacro-inspection of wafers include the following issues. The product(e.g. semiconductor wafer) can change thereby changing the expectationof what a good wafer looks like. The product is typically highlyreflective so it is difficult to illuminate without glares. A defect canbe hard to define, especially when the failure mechanism is not known.

Embodiments of the present disclosure can overcome the above challengesfor at least the following reasons. The software does not need to havebeen trained with a wafer to be able to inspect it. The software doesnot have any preset expectations for a wafer. New patterns can beinspected without any training. The illumination is diffuse, uniform andglare free. The defect is identified by a software algorithm that scansthe wafer to detect patterns, looks for areas on the wafer that breakthat pattern.

The sensitivity of the algorithm to detect defects is limited by a)non-uniformities in the patterns on the wafers that may be falselydetected as defects, b) non-uniformities of lighting that may bedetected as defects, and c) the appearance of non-uniformities due tothe interaction of the thin films on the wafer and the color of thelight. The non-uniformities that are detected as defects are abruptchanges in the pixel statistics within the spatial scale of the die.Slower changes across the wafers are not considered to be defects andare not called out as defects by the algorithm.

The first two challenges a) and b) are overcome by tuning the algorithmthat is used to detect the defects and designing a uniform lightingsystem. The last challenge c) is overcome with the use of the whitelight with a monochrome camera. FIG. 3A shows a region with a dottedline that is brighter than the rest of the wafer when illuminated by ared LED light. Referring to FIG. 3B, the same wafer when illuminatedwith a white light of the same type does not exhibit the non-uniformity.This allows the software algorithm to detect defects that are of themagnitude of this change, thus allowing the system to be more sensitive.

White Ceramic End-Effector

Embodiments of the present disclosure can include a robotic end-effectorto handle the wafer. The robotic end-effector used to present the waferto the vision inspection system can be made of a white ceramic thusallowing the notch of the wafer to be located when it is placed againstthe end-effector. When a notch is located at the edge of theend-effector it is still detectable. The robotic end-effector(especially if it is white) can reflect the light incident from the domeand minimizes the perturbation caused by its presence. The white endeffector acts as a background to the dark edge of the wafer allowing fora good contrast to detect the location of the notch. The white materialof the end effector causes a minimal perturbation in color and intensityto the incident light flux onto the dome and the wafer. The wafer can beplaced closer to the dome resulting in the increase of the lightinguniformity across the wafer.

The use of a small aperture in a lighting dome for the inspection of thesurface of a semiconductor wafer can be extended to other visionsystems. The use of back lighting with a lighting dome for theinspection of the surface of a semiconductor wafer can be extended toother vision systems. The use of a gradient reflective dome for theinspection of the surface of a semiconductor wafer can be extended toother vision systems. The use of white light with a non-monochromaticcamera for the inspection of the surface of a semiconductor wafer can beextended to other vision systems. Similarly, the use of a white ceramicend-effector for the inspection of the surface of a semiconductor wafercan be extended to other vision systems. Other systems used forinspection of materials can include polymers, glass, laminates andcomposites; and all of these systems would benefit from the use of thistechnique.

An embodiment of the present disclosure can also be included in akit-of-parts. The kit-of-parts can include some, or all, of thecomponents that an embodiment of the present disclosure includes. Thekit-of-parts can be an in-the-field retrofit kit-of-parts to improveexisting systems that are capable of incorporating an embodiment of thepresent disclosure. The kit-of-parts can include software, firmwareand/or hardware for carrying out an embodiment of the presentdisclosure. The kit-of-parts can also contain instructions forpracticing an embodiment of the present disclosure. Unless otherwisespecified, the components, software, firmware, hardware and/orinstructions of the kit-of-parts can be the same as those used in anembodiment of the present disclosure.

The particular manufacturing process used for making the dome reflectorshould be inexpensive and reproducible. Conveniently, the dome reflectorof an embodiment of the present disclosure can be carried out by usingany casting, forming or molding method. It is preferred that the processbe precise. For the manufacturing operation, it is an advantage toemploy a spin casting technique.

However, the particular manufacturing process used for making the domereflector is not essential to an embodiment of the present disclosure aslong as it provides the described functionality. Normally those who makeor use an embodiment of the present disclosure will select themanufacturing process based upon tooling and energy requirements, theexpected application requirements of the final product, and the demandsof the overall manufacturing process.

The particular material used for the dome reflector should be chemicallystable. Conveniently, the dome reflector of an embodiment of the presentdisclosure can be made of any polymer material. It is preferred that thematerial be a low molecular weight (co)polymer. For the manufacturingoperation, it is an advantage to employ a thermoplastic material.

However, the particular material selected for the dome reflector is notessential to an embodiment of the present disclosure, as long as itprovides the described function. Normally, those who make or use anembodiment of the present disclosure will select the best commerciallyavailable material based upon the economics of cost and availability,the expected application requirements of the final product, and thedemands of the overall manufacturing process.

The disclosed embodiments show a hemispherical dome as the structure forperforming the function of reflecting light toward the sample, but thestructure for reflecting light toward the sample can be any otherstructure capable of performing the function of reflecting light towardthe sample, including, by way of example an aspherical dome, a geodesicdome, a polyhedral section or at least one (a)spherical, polyhedraland/or other shape(s).

While not being limited to any particular performance indicator ordiagnostic identifier, preferred embodiments of the present disclosurecan be identified one at a time by testing for the presence of uniformillumination. The test for the presence of uniform illumination can becarried out without undue experimentation by the use of a simple andconventional light meter used to take readings at a plurality oflocating based on spherical coordinates across a section of the domereflector. Among the other ways in which to seek embodiments having theattribute of uniform illumination guidance toward the next preferredembodiment can be based on the presence of uniform reflection from aplanar homogeneous test sample.

Definitions

A semiconductor wafer is a silicon disc that has many layers ofmaterials deposited and patterned on to it. A typical wafer to beinspected by the vision system will have multitude of regions that arevisible as a pattern caused primarily by the metallic traces runningacross the wafer. The metallic traces are brighter than the silicon andother materials on the wafer.

A monochromatic light is one that is constructed with a source such asan LED that emits a narrow spectrum of light. The term light is intendedto mean frequencies greater than or equal to approximately 300 GHz, aswell as the microwave spectrum. The phrase white light source isintended to mean a source of actinic radiation with a spectral width offrom approximately 450 nm to approximately 700 nm. The phrase broadspectrum light source is intended to mean a non-monochromatic source ofactinic radiation. The phrase object holder is intended to mean a waferholder or sample space or stage such as an end-effector for asemiconductor wafer or a lighting panel cover upon which an object ofinterest can be placed.

The terms program and software and/or the phrases program elements,computer program and computer software are intended to mean a sequenceof instructions designed for execution on a computer system (e.g., aprogram and/or computer program, may include a subroutine, a function, aprocedure, an object method, an object implementation, an executableapplication, The described embodiments and examples are illustrativeonly and not intended to be limiting. Although embodiments of thepresent disclosure can be implemented separately, embodiments of thepresent disclosure may be integrated into the system(s) with which theyare associated. All the embodiments of the present disclosure disclosedherein can be made and used without undue experimentation in light ofthe disclosure. Embodiments of the present disclosure are not limited bytheoretical statements (if any) recited herein. The individual steps ofembodiments of the present disclosure need not be performed in thedisclosed manner, or combined in the disclosed sequences, but may beperformed in any and all manner and/or combined in any and allsequences. The individual components of embodiments of the presentdisclosure need not be formed in the disclosed shapes, or combined inthe disclosed configurations, but could be provided in any and allshapes, and/or combined in any and all configurations. The individualcomponents need not be fabricated from the disclosed materials, butcould be fabricated from any and all suitable materials.

Various substitutions, modifications, additions and/or rearrangements ofthe features of embodiments of the present disclosure may be madewithout deviating from the scope of the underlying inventive concept.All the disclosed elements and features of each disclosed embodiment canbe combined with, or substituted for, the disclosed elements andfeatures of every other disclosed embodiment except where such elementsor features are mutually exclusive. The scope of the underlyinginventive concept as defined by the appended claims and theirequivalents cover all such substitutions, modifications, additionsand/or rearrangements.

The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase(s) “means for” “mechanism for”and/or “step for”. Subgeneric embodiments of the invention aredelineated by the appended independent claims and their equivalents.Specific embodiments of the invention are differentiated by the appendeddependent claims and their equivalents.

What is claimed is:
 1. A method, comprising illuminating a reflectivedome having a reflectance gradient with light from a light source,wherein the reflectance gradient is a function of position relative to abase plane defined by an edge of the reflective dome; illuminating anobject substantially homogeneously with light reflected by thereflectance gradient of the reflective dome; and sensing light from theobject through an aperture in the reflective dome, wherein sensing lightfrom the object through an aperture includes sensing light from theobject through a small aperture in the reflective dome.
 2. The method ofclaim 1, wherein the reflective dome includes a shell of variablethickness that defines a gradient that increases toward the aperture toprovide the reflective gradient whereby reflectivity increases towardthe aperture.